v 1.3: Better random_choice and other library and CLI Enhancements
random_number can now accept a "step" argument as described in the docs.
Allow a short-form random_choice syntax that matches the docs.
date now casts datetimes to dates instead of returning them unchanged.
The --target-number value now allows its two sub-arguments to be specified in either order: Tablename then number or number then tablename.
The command line interface gives better error messages about unknown file extensions.
The continuation file format changed. Do not upgrade Snowfakery while running a long-running Snowfakery process. The new configuration file should be less prone to issues relating to failures to serialize results.